1. Field of the Invention
The present invention relates to an ink ribbon cassette housing an ink ribbon therein and a printing apparatus using such an ink ribbon cassette.
2. Description of the Prior Art
An ink ribbon cassette housing an ink ribbon therein is usually used in a printing apparatus which serially prints (records) characters or graphic patterns. Such an ink ribbon cassette is typically placed on a carriage to be moved thereby. In this case, the ink ribbon cassette must be held at a correct position. At the same time, the ink ribbon cassette must be light in weight, and space inside the cassette must be utilized effectively.
In an ink ribbon cassette of this type, a printing head inserting portion is generally arranged at the center of the front surface of the cassette.
Furthermore, in an ink ribbon cassette of this type, an almost exhausted state of the ink ribbon is detected to control a printing operation. More specifically, the printing operation is controlled using a ribbon end detector arranged on a carriage. The ribbon end detector includes means for photoelectrically detecting a difference in reflectivity at the ribbon end. The ribbon end detector is inserted at a position adjacent to the ribbon feed path inside the cassette. When the ribbon end is detected or after a predetermined period of time has elapsed after such detection, the printing operation is stopped to prevent poor printing.
In a conventional ribbon cassette, a printing head inserting portion is arranged at the center of the front surface of the cassette. A ribbon end detector inserting portion is arranged at a suitable position on a ribbon travel path from a supply reel to the printing head inserting position. Therefore, a length of a ribbon portion from the ribbon end detector to the printing head, i.e., the detection distance is rendered relatively short. Thus, printing cannot be continued for a predetermined period of time after detection of the ribbon end (e.g., to an end of a line, or an end of a current image portion, or the like). Printing quality without an unnatural density difference accordingly cannot be obtained.
The ribbon inside the cassette is repeatedly driven or stopped in accordance with a printing signal from a printing apparatus. Since the driving or stopping operation of the ribbon is performed abruptly, slackening or loosening of the ribbon tends to be caused. This is especially the case when the ribbon is stopped, and the supply reel continues to rotate by inertia. Even when the ribbon cassette is not used, when the ribbon cassette is moved, the supply or take-up reel is moved and similarly causes slackening of the ink ribbon. When the ribbon cassette is mounted on the printing apparatus, and such slackening of the ribbon takes place at a printing position, it is especially likely that the ribbon will be accidentally caught by the printing head. In addition, since the ribbon is not correctly located, printing quality may be degraded.
In the ink ribbon cassette, many parts are assembled within the cassette and, for this reason, the assembly is cumbersome. If an additional function is added to the cassette, the assembly becomes even more complex.
As described above, the ribbon inside the cassette is repeatedly driven or stopped in accordance with a printing signal from the printing apparatus. Since the driving and stopping operation of the ribbon is performed abruptly, slackening or loosening of the ribbon tends to be caused. This is especially the case when the ribbon is stopped, and the supply reel continues to rotate by its inertia. Even when the ribbon cassette is not used, when the ribbon cassette is moved, the supply or take-up reel is moved and similarly causes slackening of the ink ribbon. Meanwhile, in the ribbon cassette, ribbon end detection is performed ahead of the printing position along the ribbon travel path. This detection is performed optically by detecting an amount of reflected light from the travelling ribbon which is irradiated with light. When a slackening of the ribbon is caused at the ribbon end detection position, an erroneous detection is very likely to be caused.